Patient motion or motion of a living subject during imaging can cause image artifacts. The sources of motion can vary, including from restlessness, through respiration and heart beating, to small movements due to pressure changes over the cardiac cycle. In some cases motion artifacts degrade the diagnostic value of an image.
Optical methods including stereo methods for 3D measurements are known and are used to measure marker 3D position and orientation in medical imaging applications for motion correction. Generally, the patient is immobilized to limit motion during imaging. Existing measurement systems and related methods are not designed for fast motion measurement and correction.
Efficient methods for testing new drugs are very important to the pharmaceutical industry. The ability to screen test subjects for effects of a particular drug is an essential element in the process of product development. Small animals are essential for pharmaceutical testing, and mice in particular are useful for modeling human diseases. Efforts to scale down clinical medical imaging systems for smaller subjects have allowed medical researchers to obtain high-resolution computed tomography (CT) images of small animals for disease studies. Noninvasive imaging techniques, such as X-ray CT and positron emission tomography (PET), have been developed for small animal medical imaging applications. For example, small animal imaging is used in cancer research to monitor tumor growth and regression in mice.
While anatomical models are useful for studying drug effectiveness, it is very often desirable to screen test subjects for physiological effects of a drug. PET and single photon emission computed tomography (SPECT) are among current techniques used for functional medical imaging. Because test subjects must be kept alive during the screening process in order to monitor functional processes, either the animal must remain motionless for the duration of the scan or its movements must be measured and recorded with a high degree of precision and accuracy. Although sedation and physical restraint can be used to impede animal motion for this type of medical scan, both methods have the potential to alter the neurological and physiological processes that are being studied. Unrestrained awake animals tend to sometimes move rapidly. Unfortunately, as noted above, existing measurement systems are not designed for fast motion measurement and correction.